The invention relates to a method and a device for representing and monitoring function parameters of a physiological system, in particular electrocardiographic data, which are derived from electronic measuring signals.
Since the discovery of the action currents of the heart in 1887, data determined have been recorded using electrocardiography. After the initial use of the string galvanometer in conjunction with a paper strip with a light-sensitive coating for the purpose of detecting the action potentials, recording measuring units have been in use for several decades. In these measuring units, recording means comparable to a plotter execute a linear movement as a function of the amplified measured values, a paper strip being guided along perpendicular to the movement of the recording means and below the latter.
This produces a curve which has a typical, periodically repeating characteristic. With the aid of this curve, an educated and trained cardiologist can detect changes in the impulse formation, dysrhythmias or damage to the heart muscle. A disadvantage of this type of representation is that, particularly in the case of small changes, the information content can be detected only with difficulty, and that special training and wide experience are required to interpret the curves. Furthermore, a not inconsiderable period is required for careful evaluation of an electrocardiogram.
In the further development, the curve was represented on a display screen, and this rendered possible a substantially refined representation, since the electron beam has a lesser inertia than the recording unit, and therefore operates virtually without delay. A brief representation of the curve and the limited resolution on the display screen are disadvantageous here.
The two-dimensional representation led to the development of vector cardiography, in which the action currents of the heart muscle fibers are recorded in such a way that loops are produced in the three planes in space, only trained specialist staff being capable of carrying out interpretation of the space curves.
U.S. Pat. No. 5,215,099 discloses a device and a method for predicting cardiac dysrhythmias, in the case of which a multiplicity of ECG measurements of the QRS region are averaged, and atypical waveforms are rejected. The average values of the ECG measurements are subsequently digitized, the segments are shifted in time relative to one another, analyzed and transformed by means of a Fourier transformation. The transformed data are expressed in a three-dimensional form, it being possible to infer a low risk of infarct when the temporally displaced segments correspond to one another.
Various methods for representing surface potentials are described in the articles xe2x80x9cA microcomputer-based cardiac mapping system for tachycardia surgeryxe2x80x9d; Moura et al., xe2x80x9cA system for accurate interactive 3-D display of cardiac electrical activityxe2x80x9d Branham et al., xe2x80x9cA real-time data acquisition system for the display of three dimensional cardiac activation mapsxe2x80x9d; Young et al., and xe2x80x9c3-D mapping of body surface potentialsxe2x80x9d; Calderon et al.; although they permit positionally accurate assignment of the measuring points their evaluation requires experience, however.
The object of the present invention is to provide a method and device which quickly and in a fashion which can be used by anyone render it possible to analyze the variation in process states and to predict future states.
This object is achieved according to the invention by means of a method in accordance with claim 1 and a device in accordance with claim 17.
The word information microscope is illustrative both of the method according to the invention and of the device for carrying it out, since available information which is not immediately available to a viewer is brought to human perception. In the case of a light microscope, very small structures of matter are rendered visible by refraction of the light waves in a lens system. The information microscope provides function parameters of a physiological system in such a way that these are made acceptable per se to general perception, and that extremely small variations become clear.
The interpretation of complex information such as is contained, for example, in an ECG is substantially simplified and accelerated by the method according to the invention. Frequent data acquisition is possible because of the very short measuring period and the simple application, with the result that it is possible to observe a variation in a physiological system by measuring at short intervals over a long period.
The short evaluation period and the simple interpretability of the measured values provided also reveal very small variations. Predictions relating to the physiological system under investigation are possible in conjunction with the possibility of qualitatively estimating the measured values represented.
Conversion into a graphical portrait produces an individual mapping of the system under investigation with the aid of which identification is possible, as in the case of a photograph.
The graphical portrait is advantageously constructed in the manner of a three-dimensional topological model, since it is possible to transmit the highest information density with the aid of this representation, which comes closest to the natural perception of the environment. Thus, even complex measured values can be represented in a way which is graphic and easily accessible. Likewise, small deviations which could be identified only with difficulty in a two-dimensional diagram become perceptible through this type of representation because of the larger information quantity. Like a map, in which the topological conditions are visualized by an appropriate arrangement, the three-dimensional model conveys a view of the function parameters with great vividness and a high information density.
The digitization of the data permits regions previously plotted longitudinally to be assigned to space coordinates, thus achieving a three-dimensional effect. Starting from a significant measured variable, specific sections of the measured value characteristic are assigned specific spatial areas. The analog signal is digitized, and the value is used, as a function of its temporal occurrence, as an interpolation point for forming a largely closed surface. In addition, the individual interpolation points are stored with a color code which comprises both chrominance and luminance. This color code storage is performed on the basis of the measured values of in each case one analysis cycle, and permits qualitative orientation with the aid of the color values and brightness values of the image.
The analysis cycle is advantageously fixed by determining the temporal spacing of at least two repeating significant variables, the variables being a function of the physiological conditions and/or of the body part under examination. In the case of cardiological examinations, the interval between two R impulses is suggested as the length of an analysis cycle, since this is easy to determine and has a satisfactory edge steepness as a rule. The analysis cycle is fixed in this case in such a way that the significant action potentials of the heart muscle are detected, and therefore that the entire range from P to T is covered.
In order to increase the accuracy and informativeness of the measurement, and to increase the precision of the representation, it is advantageous to have a measuring period which covers a multiple of an analysis cycle. Since the discrete values of he digitized measurement correspondingly are assigned according to their sequence to specific zones inside the pictorial representation, a measurement over a time interval which contains the entire range of the values to be taken into account is favorable.
It is particularly advantageous that the assignment of color codes is calculated by combining empirically determined reference data. On the basis of data which are stored in an electronic memory and can be called up therefrom, the interpolation points are assigned information with reference to color and brightness. The assignment is performed as a function of the deviations of the measured values relative to the reference values. Depending on the extent of deviation and the position inside the curve, the measured values are assigned a corresponding color value and brightness value such that an image is produced which permits a simple diagnosis on the basis of the shape, color and brightness, because the type of information representation has been varied on the basis of medical reference data and permits simple assignment even of very small deviations.
For the purpose of not further processing evident interference signals and thereby extending the complexity of processing and reducing the accuracy of the display, a development of the invention provides a selection of the analysis cycles to be evaluated after the calculation of the autocorrelation function and of [sic] a comparison with empirically determined reference data.
In order to analyze the recorded data of an analysis cycle, they are led through a high-pass filter and digitized, and the values thus obtained are subtracted from the unfiltered data, which have likewise been digitized. The data thus obtained are combined in accordance with their value to form groups or so-called clusters such that in the case of considering a plurality of analysis circles in a time interval groups with the same value are respectively arranged adjacently in a matrix. By grouping the values, the initially irregularly distributed small fluctuations are ordered, and a regular structure with a few constant features [lacuna] from the at first glance random small fluctuations. The sequence of the grouping is individually stored for each physiological system, that is to say for each patient.
The sequence of the grouping is advantageously determined in the course of a reference measurement and applied to subsequent analysis cycles. If the renewed application of the sequence of the regrouping yields a changed structure, it is possible therefrom to infer variations in the physiological system.
In an advantageous refinement of the invention, all the analysis cycles of a time interval are taken into account when in the image calculation, since the resolution is increased by augmenting the interpolation points. The deviations present scatter the interpolation points, thus giving rise to cluster formation in the case of the evaluation of a plurality of analysis cycles.
For application in the field of individuals, in particular, it is appropriate to determine action potentials in heart examinations using a standardized 3-point recording, since a sufficient accuracy of the measurement is achieved in this way even in the case of less sensitive pick-ups. Other recordings are also provided for an application in the cardiological diagnostic field, for example the 2- or 6-point recording, the latter method delivering the most useful information on the basis of which the person skilled in the art can easily and quickly make qualitative and quantitative diagnoses.
In a development of the invention, the elimination of noise quantities is performed by correlation of the measured values of a plurality of analysis cycles. Since the occurrence of noise quantities is random in the case of recorded measured values, whereas the actual measured values are correlated with one another, the noise signals are filtered out by a correlation such that even small deviations in the image representation which would remain unrecognized in the noise in the conventional representation are detected.
In a refinement of the invention, the recorded measured values are relayed via online data lines, for example to a diagnostic center, where the data are evaluated and archived. The person to be examined need no longer be examined on the spot, but could record the data at a suitable time in the home environment, after which specialist staff evaluate them.
A development of the invention is to store the image representation with a therapy recommendation such that the dedicated interpretation of the measurement results are [sic] supported by a recommendation determined empirically.
A device with an information microscope for carrying out the method according to claim 1 has devices for data recording and conversion into electric signals, and a device for fixing an analysis cycle. Also provided is an analog-to-digital converter which digitizes the recorded data and feeds them to a storage unit. In an arithmetic unit with evaluation software connected thereto the data are provided with chrominance values and luminance values in accordance with their deviation from the data stored in the storage unit, and are assigned to a three-dimensional coordinate system. The individual values of the digitized signals form interpolation points which are connected to a closed surface. The pixels determined are conditioned for the respective output device in a control unit. The evaluation or output device transmits the image information in the form of a color picture or a color printout.
In a refinement of the information microscope, the devices for data recording are designed as electrodes, in particular as adhesive or clamping electrodes, since it is easy in this way to obtain information on action potentials of muscular activities. Precisely the clamping electrodes are easy to handle and also offer a layperson the possibility of obtaining data on a physiological system. Depending on the type of the recorded variable, use is to be made of pressure sensors, flowrate meters or optical sensors, it also being possible to use these in combination. In principle, all pickups which determine statements on physiological systems are suitable, the conversion into electric signals being performed as a function of the recorded measured value, for example in a pressure transducer or a photoelectric transducer.
Since the electric signals frequently have an excessively small amplitude, it is advantageous to provide an amplifier which can be used to provide a satisfactorily powerful signal.
Stored in the storage unit for the purpose of quick calculation of the topological model in the information microscope are empirically determined reference data which permit the values determined to be assigned either to previous measurements or to pathological changes, the storage unit advantageously being connected to the arithmetic unit, which is preferably designed as a computer.
Outputting at a monitor is particularly advantageous for uncomplicated provision of the topological model, a color monitor enhancing the informativeness of the model of the function parameters. Also provided as output medium are printers, in particular color printers, or other image-generating media such as imagers or projectors.
In a refinement of the device according to the invention, an interface for external transmission of data is provided, so that the measured values can be assessed, for example in a diagnostic center, without the need for the person examined to be present. This examination method is advantageous in the case of continuous monitoring, in particular.